1. Field
The present disclosure relates to a liquefied natural gas tank, and more particularly, to a heat-insulation structure of the liquefied natural gas tank.
2. Discussion of the Related Technology
A tank for liquefied natural gas carriers is designed to store and transport a liquefied natural gas cooled down to −175° C. and is made of stainless steel, e.g., STS304 or STS304L. The tank is constructed from an inner protection wall made of a cold insulator.
U.S. Pat. No. 6,035,795 discloses a technique of forming heat-insulating protection walls on an inner surface of a tank using a cold insulator made of sandwich foam and a glass fiber reinforced composite sheet. Korean Patent Publication No. 10-0557354B teaches a technique by which a triplex strip with a three-layered structure consisting of aluminum foils and glass fibers is bonded to a juncture of heat-insulating protection walls by means of a thermoplastic resin.
Meanwhile, in accordance with a exemplary structure for bonding heat-insulating protection walls of a liquefied natural gas carrier, a fiber-reinforced composite joint sheet is bonded to a juncture of heat-insulating protection walls in a single lap method. The bonding portion of the fiber-reinforced composite joint sheet is structurally weakest among other portions and heavily affects the strength of a bonded structure. Thus, it is of paramount importance to design and manufacture a bonded structure that can assure reliability.
In the exemplary structure for bonding heat-insulating protection walls of a liquefied natural gas carrier, however, the adhesive agent for bonding the juncture of cold insulators is very strong in brittleness. This poses a problem in that the fiber-reinforced composite joint sheets are apt to be fractured even with a light load and a liquefied natural gas may be leaked due to the fracture of the fiber-reinforced composite joint sheets.
Furthermore, a high molecular adhesive agent used in bonding the fiber-reinforced composite joint sheets is greater in thermal expansion coefficient than metal and a fiber-reinforced composite reinforcing sheet. Thus, a residual thermal stress is developed in the fiber-reinforced composite joint sheets and the adhesive agent due to the temperature difference generated during the course of charging a liquefied natural gas into a tank or discharging the liquefied natural gas from the tank. This residual thermal stress may create fine cracks and may lead to fatigue fractures. Moreover, the bonding strength becomes low if the adhesive agent is uneven in thickness, and the adhesive agent may not be applied to between the fiber-reinforced composite joint sheets, thereby reducing the bonding strength and the sealability.
The foregoing discussion is to provide general background information, and does not constitute of an admission of prior art.